Question

我想要的是将数据插入数组String []，然后打印数组值。返回的String []类型方法是

public String[] getRequirementDocIDofProject(String testprojectName)
        throws SQLException, InstantiationException, IllegalAccessException, ClassNotFoundException {
    String req_doc_ids[] = null;
    String str_sqlQuery = "select * from req_specs INNER JOIN nodes_hierarchy nh " + 
            "on nh.id=req_specs.testproject_id  " + 
            "INNER JOIN requirements reqs " + 
            "on req_specs.id =reqs.srs_id where nh.name='" + testprojectName + "'";
    int count = 0;
    int n = 0;
    initDB();
    resultSet = statement.executeQuery(str_sqlQuery);
    while (resultSet.next()){
        count = Integer.parseInt(resultSet.getString(1));
    }
    req_doc_ids = new String[count];

    resultSet = statement.executeQuery(str_sqlQuery);
    while (resultSet.next()) {
        req_doc_ids[n] = resultSet.getString("req_doc_id");
        System.out.println("REQID=" + req_doc_ids[n]);
        n++;
    }
    close();
    System.out.println("n==" + n);
    return req_doc_ids;
}

调用方法代码为

DBConnection dbcon = new DBConnection();
String req_doc_ids[] = dbcon.getRequirementDocIDofProject("XXXX");
System.out.println(req_doc_ids.length);

控制台中的打印消息为
REQID = TECH-6104
REQID = TECH-6686
REQID = TECH-5391
REQID = TECH-5965
REQID = TECH-6530
REQID = TECH-6729
REQID = TECH-7082
REQID = TECH-7107
REQID = TECH-7184
n == 9
7166

为什么req_doc_ids.length的值为7166而不是9

Answer 1

7166来自结果集的第1列-它是最后一行中的值。

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  constructor(props) {
      super(props);
      this.state = {currView: 'graph'};
  }

  handleToggle() {
      if (this.state.currView === 'graph') {
          this.setState({currView: 'otherView'});
      } else {
          this.setState({currView: 'graph'});
      }
  }

  render() {
      if(this.state.currView === 'graph') {
          // render your 'graph' view
      } else {
          // render some other view
      }
   }
}

相反，您可能是说：

while(resultSet.next()){
    count=Integer.parseInt(resultSet.getString(1));
}

请注意，这是创建数组的不必要的低效方式。请改用while(resultSet.next()){ count++; }；或者，使用结果集API上的方法直接获取行数。

Answer 2

您的主要问题已经由安迪（Andy）弄清了，这个答案只是为了帮助您使用当前代码而进行的扩展。

可以在代码中进行改进。

更喜欢使用PreparedStatement而不是Statement，这不安全，并且可能会受到Jon Skeet提到的SQL注入攻击的威胁。
为什么要运行两次数据库查询，而这可能只是为了找出正确初始化String数组的记录数而可能是一个繁重的查询。
使用List<String>存储获得的任意数量的行，最后将列表转换为数组，如下面的代码所示。
摆脱很多不必要的变量和太多行代码，使您的代码清晰明了。

您可以尝试将方法更改为此，

public String[] getRequirementDocIDofProject(String testprojectName)
        throws SQLException, InstantiationException, IllegalAccessException, ClassNotFoundException {
    List<String> reqDocIdList = new ArrayList<String>();
    String str_sqlQuery = "select * from req_specs INNER JOIN nodes_hierarchy nh " + 
            "on nh.id=req_specs.testproject_id  " + 
            "INNER JOIN requirements reqs " + 
            "on req_specs.id =reqs.srs_id where nh.name='" + testprojectName + "'";

    initDB();
    resultSet = statement.executeQuery(str_sqlQuery);
    while (resultSet.next()){
        System.out.println("REQID=" + resultSet.getString("req_doc_id"));
        reqDocIdList.add(resultSet.getString("req_doc_id"));
    }
    close();
    System.out.println("n==" + reqDocIdList.size());
    return reqDocIdList.toArray(new String[reqDocIdList.size()]);
}

java在方法String []。length中返回String []不正确

2 个答案: